Tire pressure classification based tire pressure monitoring

ABSTRACT

In indirect tire pressure monitoring of tires of a vehicle, the following steps and means to carry out the same, respectively, are contemplated:
         providing a tire classification database indicating at least one classified tire type;   determining a vehicle tire type for the vehicle on the basis of vehicle data in including information on at least one tire currently used with the vehicle;   determining whether the vehicle tire type can be associated to one of the at least one classified tire type; and,   in the case an association is determined, monitoring tire pressure according to the associated classified tire type.

FIELD OF THE INVENTION

The present invention relates to indirect tire pressure monitoring oftires of a vehicle on the basis of tire classification information.

BACKGROUND OF THE INVENTION

Monitoring of tire pressure can be assumed to become a standardfunctionality in vehicles, at least in cars and trucks, not only due togovernmental and legal regulations but also in view of a general demandfor enhanced vehicle safety.

The importance of having correct tire inflation pressure is well known.The inflation pressure directly affects, e.g., the vehicle handling, theload capacity, and the fuel consumption. There are studies that indicatethat tire related problems are the third most common reason forbreakdown of passenger vehicles. Furthermore, it has been shown that amajority of all tire flat-outs is preceded by under-inflation or slowair leakage. With tire pressure monitoring that detects the presence ofair leakages, severe accidents can thus be avoided.

Besides these well known facts about the importance of having a correctinflation pressure, tire pressure monitoring has become even moreimportant since legal regulations in some countries require all newmotor vehicles to be equipped with a system that monitors the tirepressure.

There are two alternative approaches to monitor the tire pressure. Oneway is to mount a pressure sensor inside the tire and transfer thepressure sensor value wireless to an on-board tire pressure system ofthe vehicle. This approach is referred to as “direct tire pressuremonitoring”. The other alternative, called “indirect tire pressuremonitoring”, uses existing sensors (e.g. control and/or detectiondevices of vehicles, ECUs (electronic control unit), antilock brakingsystems, dynamic stability systems, anti-spin systems and tractioncontrol systems, in form of digital and/or analog data and/or signals)to compute quantities related to the tire pressure. Indirect tirepressure monitoring is not directly measuring the air/gas pressure in atire. Rather, parameters correlated with tire pressure are calculatedusing data available from the vehicle (e.g. from brake system or theelectronic stability control system) and, on the basis of suchparameters, tire pressure is indicated.

Vehicle data commonly used in tire pressure monitoring is dataindicating an effective roll radius of wheel/tire. For the sake ofillustration, it will be referred to such wheel radius data in thefollowing.

However, there are several effects possibly influencing actual tirepressure and, thus, relation(s) between actual tire pressure and datafrom which actual tire pressure, an estimation thereof or tire pressuredeviation is to be derived.

For example, current driving situations (e.g. acceleration,deceleration; driving on smooth road surfaces vs. rough road surfaces;driving in curves etc.), temperature(s) affecting tire pressure and thelike may influence actual tire pressure and should be therefore takeinto account in indirect tire pressure monitoring.

Further, different tire types will have different properties that may bealso taken into account in indirect tire pressure monitoring. Forexample, different tires (brand, dimension, winter/summer, etc.) to someextent respond differently to changes in inflation pressure, e.g., for agiven amount of tire pressure loss, a corresponding change in e.g.effective roll radius will differ between different tires. To ensure areliable indirect tire pressure monitoring a consistent behavior ingeneral, it would be helpful to specify the behavior of the pressurerelated parameters of tire(s).

To this end, an approach may be performing in-vehicle tests where avehicle equipped with a tire type of interest is actually driven,wherein, e.g., pressure related tire behavior may be specified. However,such an approach will be time-consuming and expensive.

OBJECT OF THE INVENTION

The object of present invention is to improve indirect tire pressuremonitoring such that tire related effects may be taken into account in amore easy and technically and economically feasible manner.

SUMMARY OF THE INVENTION

To solve the above object, the present invention provides a method, asystem and a computer program product as defined in the independentclaims.

According to a first aspect the present invention provides method ofindirect tire pressure monitoring of tires of a vehicle, which methodcomprises the steps of:

-   -   providing a tire classification database indicating at least one        classified tire type;    -   determining a vehicle tire type for the vehicle on the basis of        vehicle data in including information on at least one tire        currently used with the vehicle;    -   determining whether the vehicle tire type can be associated to        one of the at least one classified tire type; and,    -   in the case an association is determined, monitoring tire        pressure according to the associated classified tire type.

According to another aspect, the present invention provides a system forindirect tire pressure monitoring of tires of a vehicle, comprising:

-   -   a tire classification database indicating at least one        classified tire type;    -   a vehicle tire type determination unit being adapted to        determine a vehicle tire type for the vehicle on the basis of        vehicle data in including information on at least one tire        currently used with the vehicle;    -   an association determination unit being adapted to determine        whether the vehicle tire type can be associated to one of the at        least one classified tire type; and    -   a tire pressure monitoring unit being adapted to, in the case an        association is determined, monitor tire pressure according to        the associated classified tire type.

In a still further aspect, the present invention provides computerprogram product, the computer program product comprising program codefor carrying out, when executed on a processing system, the steps of:

-   -   providing a tire classification database indicating at least one        classified tire type;    -   determining a vehicle tire type for the vehicle on the basis of        vehicle data in including information on at least one tire        currently used with the vehicle;    -   determining whether the vehicle tire type can be associated to        one of the at least one classified tire type; and,    -   in the case an association is determined, monitoring tire        pressure according to the associated classified tire type.

Further aspects, features and advantages of the present invention willbecome apparent from the below description, the accompanying drawingsand the appended claims.

SHORT DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleand with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates an indirect tire pressure monitoringsystem according to an embodiment of the present invention;

FIG. 2 schematically illustrates forces considered in tireclassification according to the present invention; and

FIG. 3 shows graphs schematically illustrating wheel speed spectrum dataand tire force spectrum data.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a system according to the presentinvention, particularly in form of a tire pressure deviation (TPD)warning system 2 using indirect tire pressure monitoring.

The present invention is provided for use in any kind of vehicle havingat least one wheel equipped with at least one tire. The term “vehicle”as used herein comprises any type of vehicle, such as cars, bikes,trucks, trailers, and the like, where information on the basis of whichindirect tire pressure monitoring is possible.

A “pressure deviation” in a tire may be detected if the tire pressureactually determined for the tire differs from anormal/predefined/desired tire pressure and/or differs from the pressureof one or more other tires by a predetermined threshold value.

As used herein, “on the basis of . . . ” and “based on . . . ” indicatethat at least the “. . . ” is used as basis and should not be construedto be limited to the “. . . ”, for example, “on the basis of the atleast one vehicle data” indicates that at least the at least one vehicledata are used and that further, e.g., data and/or information may beused.

Further, the present invention may use vehicle data on the basis ofwhich tire pressure monitoring is possible. Contemplated vehicle datainclude at least one of:

-   -   vehicle data indicative of ambient temperature;    -   vehicle data indicative of a temperature of an engine of the        vehicle;    -   vehicle data indicative of an engine torque of an engine of the        vehicle;    -   vehicle data indicative of a torque acting on the at least one        tire;    -   vehicle data indicative of a engine speed of an engine of the        vehicle;    -   vehicle data indicative of a yaw rate of the vehicle;    -   vehicle data indicative of a speed of the vehicle;    -   vehicle data indicative of at least one of a lateral        acceleration and a longitudinal acceleration of the vehicle;    -   vehicle data indicative of a steering wheel angle of a steering        wheel of the vehicle;    -   vehicle data indicative of a driving condition of the vehicle,        particularly a braking condition;    -   vehicle data indicative that a gear shift of the vehicle is in        progress;    -   vehicle data indicative that a braking system of the vehicle is        operating;    -   vehicle data indicative of brake pressure; and    -   vehicle data indicative that at least one active control device        of the vehicle is active.

However, before continuing with descriptions of the drawings, somefurther observations to further aspects of the present invention aregiven. More detailed observation to the method related aspects of thepresent invention also apply to corresponding system related aspects andcomputer program related aspects of the present invention even if notexplicitly noted.

In the method of the present invention, the tire classification databasemay indicate, in association to each of the at least one classified tiretype, at least one of at least one parameter setting for tire pressuremonitoring and at least one operation mode for tire pressure monitoring;wherein the method of the present invention may further comprise a stepof retrieving at least one of the at least one parameter setting and atleast one operation mode from the tire classification database, whereinthe step of tire pressure monitoring is performed according to theretrieved at least one parameter setting and operation mode.

For example, if a tire has been classified (e.g. by precise parametersor at least a rough assignment to a respective group/type of tires),classification information may be used for, e.g., controlling/selectinga size of calibration slots in roll radius based indirect tire pressuremonitoring (e.g. using wheel/tire radius analysis) and/or wheel/tirespectrum analysis, how much data should be used in each slot, adaptationspeeds in roll radius based indirect tire pressure monitoring (e.g.using wheel/tire radius analysis) and/or wheel/tire spectrum analysis,indicators, warning thresholds, timers, sensitivity levels etc.

In the method of the present invention the step of determining thevehicle tire type may include a step of determining an overall vehicletire type for the vehicle.

An overall vehicle tire type may indicate a tire type common to allvehicle tires or may be a “virtual” tire type (e.g. based oncomputations of information on vehicle tires of the same type) havingproperties, characteristics and, particularly, pressure related behaviorat least partially suitable and/or acceptable for all vehicle tiresirrespective of their actual types.

In such embodiments, the step of tire pressure monitoring may beperformed for at least two different tires of the vehicle according tothe associated classified tire type. For example, a single associatedclassified tire type may be used as basis for tire pressure monitoringfor all vehicle tires.

In the method of the present invention, the step of determining thevehicle tire type may be performed to determine an individual vehicletire type for at least two different tires of the vehicle.

An individual vehicle tire type may be the actual tire type of a tirebeing of interest (e.g. to be tire pressure monitored).

In such embodiments, the step of determining whether the vehicle tiretype can be associated to one of the at least one classified tire typemay be performed with respect to each of the at least two differenttires.

Further, the step of tire pressure monitoring may be performed for eachof the at least two different tires according to the respectivelyassociated classified tire type. For example, for each vehicle tiretype, an associated classified tire type may be used as basis for tirepressure monitoring for all vehicle tires, i.e. more than one associatedclassified tire types may be used.

In the method of the present invention, the step of determining thevehicle tire type may include a step of determining at least onecharacteristic of a tire of the vehicle; and the step of determiningwhether the vehicle tire type can be associated to one of the at leastone classified tire type may include a step of determining whether oneof the at least one classified tire type have at least onecharacteristic being at least comparable with the determined at leastone vehicle tire characteristic.

In the method of the present invention, the step of determining thevehicle tire type may include a step of wheel speed spectrum analysis toobtain a wheel speed spectrum data for the at least one tire.

In such embodiments, the step of determining whether the vehicle tiretype can be associated to one of the at least one classified tire typemay include a step of determining whether the tire classificationdatabase includes data indicating a tire type having tire force spectrumdata being at least comparable with the wheel speed spectrum data.

In the method of the present invention, the step of wheel spectrumanalysis may include a step of determining wheel speed resonance centerof gravity data for the at least one tire.

In such embodiments, the step of determining whether the vehicle tiretype can be associated to one of the at least one classified tire typemay include a step of determining whether the tire classificationdatabase includes data indicating a tire type having a tire forceresonance center of gravity data being at least comparable with thewheel speed resonance center of gravity data.

In the method of the present invention, the step of wheel spectrumanalysis may include a step of determining wheel speed resonance widthdata for the at least one tire.

Here, step of determining whether the vehicle tire type can beassociated to one of the at least one classified tire type may include astep of determining whether the tire classification database includesdata indicating a tire type having a tire force resonance width databeing at least comparable with the wheel speed resonance width data.

The method of the present invention may further include a step ofgenerating the tire classification database on the basis of testing atleast one to be classified tire in a test environment.

In such embodiments, the step of generating the tire classificationdatabase may include a step of determining, for the at least one to beclassified tire, data indicating characteristic tire oscillations.

According to the method of the present invention, the step of generatingthe tire classification database may include a step of determining, forthe at least one to be classified tire, data indicating tireoscillations in tangential tire direction.

Further in the method of the present invention, the step of generatingthe tire classification database may include a step of determining, forthe at least one to be classified tire, data indicating tireoscillations in radial tire direction.

In the method of the present invention, the step of generating the tireclassification database may include a step of determining, for the atleast one to be classified tire, tire force spectrum data.

In the method of the present invention, the step of generating the tireclassification database may include a step of determining, for the atleast one to be classified tire, tire force resonance center of gravitydata.

In the method of the present invention, the step of generating the tireclassification database may include a step of determining, for the atleast one to be classified tire, tire force resonance width data.

In the method of the present invention, the step of determining tireforce spectrum data may be based on the data indicating tireoscillations in tangential tire direction; and/or the step ofdetermining tire force resonance center of gravity data may be based onthe data indicating tire oscillations in tangential tire direction;and/or the step of determining tire force resonance width data may bebased on the data indicating tire oscillations in tangential tiredirection.

In the method of the present invention, the step of determining tireforce spectrum data may be based on the data indicating tireoscillations in radial tire direction; and/or the step of determiningtire force resonance center of gravity data may be based on the dataindicating tire oscillations in radial tire direction; and the step ofdetermining tire force resonance width data may be based on the dataindicating tire oscillations in radial tire direction.

In the method of the present invention, the step of generating the tireclassification database may include a step of determining, for the atleast one to be classified tire, at least one of at least one parametersetting for indirect tire pressure monitoring and at least one operationmode for indirect tire pressure monitoring.

In the method of the present invention, in the case the step ofdetermining whether the vehicle tire type can be associated to one ofthe at least one classified tire type fails, the step of tire pressuremonitoring may be performed on the basis of at least one of a defaultparameter setting and a default operation mode.

In the system of the present invention, the tire classification databasemay indicate, in association to each of the at least one classified tiretype, at least one of at least one parameter setting for tire pressuremonitoring and at least one operation mode for tire pressure monitoring;wherein the system of the present invention may further comprise aretrieving unit being adapted to retrieve at least one of the at leastone parameter setting and at least one operation mode from the tireclassification database, wherein the tire pressure monitoring unit maybe adapted to perform fire pressure monitoring according to theretrieved at least one parameter setting and operation mode.

In the system of the present invention, the vehicle tire typedetermination unit may be adapted to determine an overall vehicle tiretype for the vehicle.

Here, the tire pressure monitoring unit may be adapted to perform tirepressure monitoring for at least two different tires of the vehicleaccording to the associated classified tire type.

In the system of the present invention, the vehicle tire typedetermination unit may be adapted to determine an individual vehicletire type for at least two different tires of the vehicle,

In such embodiments, the association determination unit may be adaptedto determine whether the vehicle tire type can be associated to one ofthe at least one classified tire type with respect to each of the atleast two different tires.

Further, the tire pressure monitoring unit may be adapted to per formtire pressure monitoring for each of the at least two different tiresaccording to the respectively associated classified tire type.

In the system of the present invention, the vehicle tire typedetermination unit may be adapted to determine at least onecharacteristic of a tire of the vehicle; and the associationdetermination unit may be adapted to determine whether one of the atleast one classified tire type has at least one characteristic being atleast comparable with the determined at least one vehicle tirecharacteristic.

In the system of the present invention, the vehicle tire typedetermination unit may be adapted to perform wheel speed spectrumanalysis to obtain a wheel speed spectrum data for the at least onetire.

Here, the association determination unit may be adapted to determinewhether the tire classification database includes data indicating a tiretype having tire force spectrum data being at least comparable with thewheel speed spectrum data.

According to the present invention, the association determination unitmay be adapted to determine wheel speed resonance center of gravity datafor the at least one tire.

Then, the vehicle tire type determination unit may be adapted todetermine whether the tire classification database includes dataindicating a tire type having a tire force resonance center of gravitydata being at least comparable with the wheel speed resonance center ofgravity data.

In the system of the present invention, the association determinationunit may be adapted to determining wheel speed resonance width data forthe at least one tire.

In such embodiments, the vehicle tire type determination unit may beadapted to determine whether the tire classification database includesdata indicating a tire type having a tire force resonance width databeing at least comparable with the wheel speed resonance width data.

The system of the present invention may further include means beingadapted to carry out the steps set forth above with respect togeneration of the tire classification database.

Further, in the system of the present invention, in the case the vehicletire type can be associated to one of the at least one classified tiretype fails, the tire pressure monitoring unit may be adapted to performtire pressure monitoring on the basis of at least one of a defaultparameter setting and a default operation mode.

The computer program product of the present invention may furthercomprise program code for carrying out, when executed on a processingsystem, the steps of at least, one of the above-mentioned possibleembodiments of the method of the present invention.

The computer program product of the present invention may be stored on acomputer readable storage medium or in a computer-readable storagedevice.

Now, referring to the drawings again, FIG. 1 schematically illustrates aprinciple system arrangement according to the present invention,particularly in form an tire pressure deviation (TPD) warning system 2.

The TPD warning system 2 may for example be a hardware and/or softwarecomponent, which is integrated in an electronic control unit (e.g. ECU)of a vehicle. The system 2 obtains so-called vehicle data by means of aninterface unit 4, which may be—in the case of an at least partiallysoftware based implementation—an application program interface (API).The vehicle data may include vehicle signals from the vehicle CAN buse.g. describing the vehicle condition. The vehicle data may (further)include measuring data, information, signals and the like directlyobtained and/or indirectly derived from vehicle's sensors, such asrotational speed sensors (as existent in the vehicle's ABS), whichindicate angular velocities of rotating wheels and tires, respectively.

In particular, the vehicle data may be indicative of ambienttemperature, temperature of an engine of the vehicle, wheel/tire angularvelocity, wheel/tire rotational speed, engine torque of an engine of thevehicle, torque acting on the at least one tire, engine speed of anengine of the vehicle, yaw rate of the vehicle, speed of the vehicle,lateral and/or longitudinal acceleration of the vehicle, steering wheelangle of a steering wheel of the vehicle, of a driving condition of thevehicle, particularly a braking condition, gear shift of the vehiclebeing in progress and an active control device of the vehicle beingactively operating.

Any of such data may be used by units for determining tire pressureindicating data, which units are described below. However, inembodiments described here, particularly, wheel/tire angular velocityand/or wheel/tire rotational speed may be used for tire pressuredetermination and can be considered as an example for informationindirectly indicating tire pressure.

To provide such vehicle data, an ECU and/or sensors of the vehicle maybe used. For example, temperature sensor(s), yaw rate sensor(s), torquesensor(s), speed sensor(s), accelerator sensor(s), and/or sensorsindicating accelerator pedal, clutch pedal and/or braking pedalposition(s) ray be employed to acquire vehicle data and/or to performmeasurements on the basis of which vehicle data may be derived.

The vehicle data may directly provided to units of system 2 and/or maybe stored in a memory unit 6 for later use.

A diagnosis control unit 8 performs internal system and input signalchecks and sets system status and error codes, which may be consideredas device status data and/or error indicating data. If a severe erroroccurs, this unit can disable the system 2.

Obtained vehicle data may be input to a preprocessing unit 10, which mayprocess (e.g. filters) vehicle data, for example, to remove disturbancesand offsets, and may pre-compute vehicle data such that they can be usedby other system parts.

Signals output by preprocessing unit 10 are input to a unit for rollradius based indirect tire pressure monitoring, here exemplarily in formof a wheel radius analysis (WRA) unit 12, and/or a wheel spectrumanalysis (WSA) unit 14. To WRA unit 12 and a WSA unit 14 will beprovided vehicle data (unprocessed and/or processed by preprocessingunit 10) at least indicating wheel/tire angular velocity and/orwheel/tire rotational speed. Further vehicle signals may be related towheel/tire angular velocity “energy”, yaw rate, yaw rate from wheel/tirevelocity, engine torque, braking in progress, reverse driving inprogress, active control in progress, vehicle speed, longitudinalacceleration, lateral acceleration, wheel slip, normalized tractionforce, gear shift in progress, data quality indicators (dynamic driving,slip variance, etc.), ambient temperature and vehicle status.

In some embodiments, WRA unit 12 and WSA unit 14 may be further provideddata indicating, e.g., special driving conditions (e.g. driving withsnow chains, on rough roads, on oval track and in a roundabout etc.).Such data may be generated by a dynamic state detector unit 16 based onvehicle data from interface 4, memory 6 and/or preprocessing unit 10.Thus, data from dynamic state detector unit 16 may be also referred toas vehicle data as they are derived there from and can be considered asdriving situation/scenario indicating data according to some embodimentsof the present invention.

Wheel radius analysis as executed in the WRA unit 12 are based on thefact that the wheel speed of a wheel depends on the respective wheelradius: the wheel speed increases with decreasing wheel radius. Changesin the wheel radius contain information about changes in the tirepressure of the corresponding wheels, but may also reflect, e.g.,vehicle load changes and surface changes or react on driving forces(acceleration, braking, forces in curves etc.). WRA unit 12 may detectrelative changes in tire pressure with respect to at least two tires.

Based on the wheel angular velocity signals, WSA unit 14 detects changesin the spectral properties of each of the four wheel angular velocitysignals. The tire pressure has significant influence on thecharacteristics of the spectrum of the angular velocity signal; however,further conditions (e.g. driving situation, road surface andtemperature) may also have an impact on the angular velocity signalspectrum and may be therefore considered.

WSA unit 14 may detect changes in tire pressure for each wheelindividually, for example by calculating a parametric model of thewheel/tire velocity spectrum and using the parameters of this model tocalculate a spectral shape factor that condenses the different pressuredependent features of the spectrum into one single scalar quantity.

In further embodiments, WSA unit 14 may use DFT-based approach(es) ormethod(s) to determine wheel/tire spectrum.

According to embodiments described here, WSA unit 14 may be consideredas implementation of the step of determining the vehicle tire typeand/or the vehicle tire type determination unit or at least a part ofsuch an implementation; in the latter case below described combinationunit 18 may be considered as implementation of remaining parts.

In addition or as alternative, WSA unit 14 may be considered asimplementation of the step of tire pressure monitoring and/or the tirepressure monitoring unit or at least a part of such an implementation;in the latter case below described combination unit 18 may be consideredas implementation of remaining parts. Tire pressure indicating data mayprovided by WRA unit 12 only or by WSA unit 14 only or by both WRA unit12 and WSA unit 14,

A combination unit 18 obtains data from WRA unit 12 and/or WSA unit 14and from interface unit 4, memory unit 6 and/or preprocessing unit 10.According to described embodiments, data generated by combination unit18 may be considered as implementation of tire pressure condition data.

More specifically, data provided to combination unit 18 include tirepressure deviation data of at least one of WRA unit 12 and WSA unit 14.Such data will be used to determine tire pressure condition dataindicative of tire pressure deviation condition(s) for the vehicle tire.To this end, combination unit 18 may also use data indicating, e.g.,special driving conditions (e.g. driving with snow chains, on roughroads, on oval track and in a roundabout etc.) provided by dynamic statedetector unit 16 and/or further vehicle data.

In general, combination unit 18 determines, based on input data, tirepressure deviation condition(s) for each tire separately or for at leasttwo tires together. In embodiments not illustrated, combination unit 18determines whether tire pressure indicating data indicate a deviationfrom a preset, desired and/or required tire pressure. To this end,combination unit 18 may additionally take into account further inputdata, such as data representing a current driving situation, since suchdata may influence a decision whether an inappropriate tire pressuredeviation exists. Such determination(s) may use threshold comparison(s).Then, an inappropriate tire pressure deviation may be ascertained in thecase tire pressure indicating data violate an upper and/or lowerthreshold (e.g. maximally and minimally, respectively, allowable tirepressure).

If an inappropriate tire pressure deviation condition is detected,combination unit 18 may generate warning data, enable a warning signaland the like to inform about the inappropriate tire pressure deviationcondition.

According to embodiments described here, combination unit 18 may beconsidered as implementation of the step of determining the vehicle tiretype and/or the vehicle tire type determination unit or at least a partof such an implementation; in the latter case WSA unit 14 may beconsidered as implementation of remaining parts.

In addition or as alternative, combination unit 18 may be considered asimplementation of the step of determining whether a vehicle tire typecan be associated to one of the at least one classified tire type and/orthe association determination unit, or at least a part of such animplementation; in the latter case WSA unit 14 may be considered asimplementation of remaining parts.

As set forth above, different tire types may exhibit different tirepressure related behaviors. For optimization, indirect tire pressuremonitoring is, according to the present invention, adapted to take intoaccount different tire types. In general, the present invention teachesto determine the type of a vehicle tire to be indirectly tire pressuremonitored, to determine whether the determined vehicle tire type can beassociated to a previously classified tire type and, in the case such anassociation can be made, to indirectly tire pressure monitor the vehicletire in question according to the associated classified tire type.

In the following, embodiments for classification of tire types areexplained with reference to FIG. 2.

Tire to be classified were mounted in a test rig for performing forcespectrum analysis in order to obtain information on characteristicoscillations of a tested tire. A tire belt oscillates in the tangentialdirection due to force variations in the contact area with the ground(e.g. when it hits a small obstacle). This force can be measured in thelongitudinal direction of the hub, when the tire is mounted in a rig(force equilibrium); see FIG. 2 a. The tire also oscillates in atranslational motion as a spring-damper system, when compressed by thecleat. This force can be measured in the vertical direction, of the hub,see FIG. 2 b.

Actual experiments have shown that the first eigenfrequency of thetangential mode and the first eigenfrequency of the translational modeare legible at different velocities. For example, in some experimentsfirst eigenfrequency of the tangential mode is most legible at lowvelocities (30 km/h), while the first eigenfrequency of thetranslational mode is most legible at higher velocities (90 km/h).

In some embodiments, for estimation of power spectrum of the tireforces, force data is down sampled to 400 Hz and segmented so that eachsegment contains data from one drum revolution (or one cleat impact).The segments are zero padded to be of length 1024 samples and windowedto eliminate leakage from transients. The periodogram (power spectrumestimate) is calculated according to Welch's method:

${\Phi (\omega)} = {\frac{1}{R}{\sum\limits_{k = 1}^{R}{\Phi_{M}^{(k)}(\omega)}}}$

where R is the number of segments of length M (here M=1024), and

${\Phi_{M}^{(k)}(\omega)} = {\frac{T}{M}{{{FFT}\left( {F_{k}(t)} \right)}}^{2}}$

where Fk(t) is the k:th segment.

Changes in a power spectrum of tire forces may be characterized by thefollowing terms:

Resonance center of gravity f_(cog):

${f_{cog} = \frac{\int_{f_{low}}^{f_{high}}{f*{P_{xx}(f)}{f}}}{\int_{f_{low}}^{f_{high}}{{P_{xx}(f)}{f}}}},$

where Pxx(f) is the power spectrum for a tire xx and f_(low) andf_(high) indicate lower and upper, respectively, frequencies defining afrequency band of interest.

Resonance width w:

$w = \sqrt{\frac{\int_{f_{low}}^{f_{high}}{\left( {f - f_{cog}} \right)^{2}*{P_{xx}(f)}}}{\int_{f_{low}}^{f_{high}}{{P_{xx}(f)}{f}}}}$

The spectral features f_(cog) and w were computed for each powerspectrum estimate in order to generate feature trajectory plots.

In some embodiments, the following frequency boundaries have been used:

For tire forces in tangential tire direction:

f_(low)=20 Hz

f_(high)=50 Hz

For tire forces in tangential tire direction:

f_(low)=60 Hz

f_(high)=120 Hz

Analysis of trajectories of spectral features f_(cog) and w for powerspectrum estimates of tested tire(s) in view of results obtained fromin-vehicle tests of the same tire(s) demonstrated that a tire forcespectrum obtain from a tire in a test rig and, particularly, itsspectral features f_(cog) and w is correlated to a wheel speed spectrumof the same tire obtained in in-vehicle experiments and, respectively,to the spectral features f_(cog) and w obtained for the wheel speedspectrum. Such a wheel speed spectrum may be provided by above WSA unit14.

FIG. 3 shows graphs schematically illustrating wheel speed spectrum data(FIG. 3( a)) and tire force spectrum data (FIG. 3( b)). Each of theillustrated curves includes data obtained for different tire pressures.As can been seen, each of the tire types 368, 362 and 328 have at leastcomparable wheel speed spectrum data and tire force spectrum data andalso have at least comparable pressure dependent behavior. Thus, havinginformation like that illustrated in FIG. 3( b) allows to determinewhether a vehicle tire to tire pressure monitored in actual use can beassociated to a previously classified tire type (e.g. in the illustratedexample, whether a vehicle tire to tire pressure monitored is tire type368, 362 or 328).

As a result, tire force spectrum analysis of a tire in a test rig, e.g.performed as set forth above, provides information on the behavior ofthat tire when mounted on a vehicle under actual driving conditions.

Correlation of tire force spectrum obtained from test rig experiments(and its spectral features f_(cog) and w) and wheel speed spectrum (andits spectral features f_(cog) and w) may be, e.g., readily apparent dueto comparable features trajectories (in scaled or un-scaled form), e.g.as demonstrated in FIG. 3, and/or obtained on the basis of neuronalnetwork techniques.

On the basis of such correlation(s), it is possible to determine anassociation of a tire currently used on a vehicle and a tire classifiedby test rig experiments.

Further, test rig experiments and verification thereof based onin-vehicle tests have shown chat tire force spectrum also indicateswhether a tire will be easily indirectly tire pressure monitored or not.Even more, it is possible to discriminate in greater detail simplicityand/or complexity of tire pressure monitoring for different tire types,e.g., tires that may be tire pressure monitored with a low, anintermediate or a high degree of complexity.

Such information on a tire type may be used to pre-define parametersetting(s) and/or operation mode(s) to be used in tire pressuremonitoring a tire of that type in actual use on a vehicle.

With respect to possible parameter settings it is noted that (forexample, as known from e.g wheel/tire spectrum analysis) tires responddifferently. For example, stiffer tires may react with reduced/increasedamplitude for changed tire pressure and softer tires may react with afrequency shift. With a soft tire the response may be so large that theparameters need to be less sensitive to avoid false alarms. For sometires one or more modules of TPI may even be deactivated to improverobustness. Starting therefrom, it is therefore beneficial, when itcomes to different parameter settings for different tires, to employsuitable tire response characteristics for tire to be monitored.

Information obtained in such experimental environment(s) may be providedin form of a database, which may be implemented in and/or associated tothe above system 2 (e.g. memory unit 6, WSA unit 14, and/or combinationunit 18).

In the following, embodiments of tire pressure monitoring using such adatabase are described, wherein reference is made to above system 2 forillustration purposes only. Further, it is noted that, since WSA unit 14is capable of providing information indicating individual tire pressure,the following procedure may be preformed for a single vehicle tire, morethan one vehicle tire and up to all vehicle tires.

In use, WSA unit 14 determines wheel speed spectrum data of each vehicletire to monitored. The wheel speed spectrum data may be determined for,e.g., a specific vehicle speed, a vehicle speed range, a specific wheelspeed, a wheel speed range etc.

Further, spectral features f_(cog) and w of the determined wheel speedspectrum data may be determined.

On the basis of the wheel speed spectrum data and/or its spectralfeatures f_(cog) and w, it is ascertained whether the tireclassification database comprising information on previously classifiedtire types includes tire force spectrum data and/or respective spectralfeatures f_(cog) and w of a previously classified tire type to which thewheel speed spectrum data and/or its spectral features f_(cog) and w maybe associated.

In the case the database does not include such information (e.g. thevehicle tire to be monitored has not been previously classified, has notbeen included in the tire classification database etc), system 2 isnormally operated. Normal operation may be based on default parametersetting(s) and/or operation mode(s) for tire pressure monitoring; suchdefault information may be implemented in system 2 itself or may beprovided by the tire classification database.

In the latter case, the tire classification database may includeinformation indicating a default classification tire. A defaultclassification tire may be specified on the basis of, e.g., empirical,statistical, model based consideration.

Default parameter setting(s) and/or operation model(s) for a defaultclassification tire may be defined to provide for an optimal tomonitoring of a plurality of different tire types (e.g. tire typescommon on the market, tire types usually used with the vehicle, tiretypes recommended for the vehicle etc.).

In the case an association of vehicle tire(s) and a classified tire canbe made (particularly, an association of the spectrum data and theirspectral features f_(cog) and w), system 2 retrieves from the tireclassification database parameter setting(s) and/or operation mode(s)previously defined for tire pressure monitoring of the identifiedclassified tire type. Retrieved parameter setting(s) and/or operationmodels), which may be as set forth above, are then used by system 2 inactual tire pressure monitoring of vehicle tire(s).

If system 2 determines that the vehicle is equipped with tires of two ormore different types, the forgoing procedure (e.g. determination whethera classified tire type can be associated, retrieval of parametersetting(s) and or operation mode(s), tire pressure monitoring accordingto retrieved parameter setting(s) and/or operation mode(s)) mayperformed for each vehicle tire type separately (in parallel orsubsequently).

In cases of two or more different vehicle tire types it is also possibleto determine a so-called, overall vehicle tire type, e.g. a virtual tireaccommodating at least some properties of all actual tire types(particularly, their pressure dependent behavior). An overall vehicletire type may be obtained by computing, on the basis of wheel spectrumdata for different actual tire types, wheel spectrum data to be used foridentifying a classified tire type to be associated to all actual tiretypes. Such computed wheel spectrum data may be derived by means ofaveraging, median and/or weighting techniques and/or the like.

1-44. (canceled)
 45. A method of indirect tire pressure monitoring oftires of a vehicle, comprising: providing a tire classification databaseindicating at least one classified tire type; determining a vehicle tiretype for the vehicle on the basis of vehicle data in includinginformation on at least one tire currently used with the vehicle;determining whether the vehicle tire type can be associated to one ofthe at least one classified tire type; and in the case an association isdetermined, monitoring tire pressure according to the associatedclassified tire type, wherein, determining whether the vehicle tire typecan be associated to one of the at least one classified tire type fails,tire pressure monitoring is performed on the basis of at least one of adefault parameter setting and a default operation mode.
 46. The methodof claim 45, wherein the tire classification database indicates, inassociation to each of the at least one classified tire type, at leastone of at least one parameter setting for tire pressure monitoring andat least one operation mode for tire pressure monitoring; and furthercomprising retrieving at least one of the at least one parameter settingand at least one operation mode from the tire classification database,wherein tire pressure monitoring is performed according to the retrievedat least one parameter setting and operation mode; and/or whereindetermining the vehicle tire type includes determining an overallvehicle tire type for the vehicle, wherein tire pressure monitoring ispreferably performed for at least two different tires of the vehicleaccording to the associated classified tire type; and/or whereindetermining the vehicle tire type is performed to determine anindividual vehicle tire type for at least two different tires of thevehicle; and/or wherein determining whether the vehicle tire type can beassociated to one of the at least one classified tire type is performedwith respect to each of the at least two different tires; and/or whereintire pressure monitoring is performed for each of the at least twodifferent tires according to the respectively associated classified tiretype; and/or wherein determining the vehicle tire type includesdetermining at least one characteristic of a tire of the vehicle; anddetermining whether the vehicle tire type can be associated to one ofthe at least one classified tire type includes determining whether oneof the at least one classified tire type has at least one characteristicbeing at least comparable with the determined at least one vehicle tirecharacteristic.
 47. The method of claim 45, wherein determining thevehicle tire type includes wheel speed spectrum analysis to obtain awheel speed spectrum data for the at least one tire.
 48. The method ofclaim 47, wherein determining whether the vehicle tire type can beassociated to one of the at least one classified tire type includesdetermining whether the tire classification database includes dataindicating a tire type having tire force spectrum data being at leastcomparable with the wheel speed spectrum data; and/or wherein wheelspectrum analysis includes determining wheel speed resonance center ofgravity data for the at least one tire, wherein determining whether thevehicle tire type can be associated to one of the at least oneclassified tire type preferably includes determining whether the tireclassification database includes data indicating a tire type having atire force resonance center of gravity data being at least comparablewith the wheel speed resonance center of gravity data; and/or whereinwheel spectrum analysis includes determining wheel speed resonance widthdata for the at least one tire, wherein determining whether the vehicletire type can be associated to one of the at least one classified tiretype preferably includes determining whether the tire classificationdatabase includes data indicating a tire type having a tire forceresonance width data being at least comparable with the wheel speedresonance width data.
 49. The method of claim 45, further includinggenerating the tire classification database on the basis of testing atleast one to be classified tire in a test environment.
 50. The method ofclaim 49, wherein generating the tire classification database includesdetermining, for the at least one to be classified tire, data indicatingcharacteristic tire oscillations; and/or wherein generating the tireclassification database includes determining, for the at least one to beclassified tire, data indicating tire oscillations in tangential tiredirection; and/or wherein generating the tire classification databaseincludes determining, for the at least one to be classified tire, dataindicating tire oscillations in radial tire direction; and/or whereingenerating the tire classification database includes determining, forthe at least one to be classified tire, tire force spectrum data; and/orwherein generating the tire classification database includesdetermining, for the at least one to be classified tire, tire forceresonance center of gravity data; and/or, wherein generating the tireclassification database includes determining, for the at least one to beclassified tire, tire force resonance width data; and/or whereindetermining tire force spectrum data is based on the data indicatingtire oscillations in tangential tire direction; determining tire forceresonance center of gravity data is based on the data indicating tireoscillations in tangential tire direction; and determining tire forceresonance width data is based on the data indicating tire oscillationsin tangential tire direction; and/or wherein determining tire forcespectrum data is based on the data indicating tire oscillations inradial tire direction; determining tire force resonance center ofgravity data is based on the data indicating tire oscillations in radialtire direction; and determining tire force resonance width data is basedon the data indicating tire oscillations in radial tire direction;and/or wherein generating the tire classification database includesdetermining, for the at least one to be classified tire, at least one ofat least one parameter setting for indirect tire pressure monitoring andat least one operation mode for indirect tire pressure monitoring.